Methods such as isolation culture, PCR, ELISA, EIA, Western blotting, and immunochromatography, are generally known as methods for detecting influenza virus. Since influenza virus is a seasonal pathogen, many patients with influenza visit hospitals in a short period, and a large number of viral tests are carried out in the short period at actual clinical sites. Therefore, immunochromatography is recently becoming common at medical sites because of its rapidness and simplicity.
As common methods of immunochromatography, methods using membranes such as nitrocellulose membranes are known. In these methods, a ligand that specifically binds to the substance to be detected is immobilized on a membrane, and this ligand captures, through the substance to be detected, a complex containing a labeled substance in which a ligand that specifically binds to the substance to be detected is labeled, thereby allowing an assay on the presence or absence of the substance to be detected in the sample. The labeled substance is generally a ligand which specifically binds to the substance to be detected and which is labeled with an enzyme such as alkaline phosphatase, with a colloidal metal such as colloidal gold, or with a colored polystyrene particle prepared by staining with a dye. In particular, a colloidal gold particle or a colored polystyrene particle is used in many cases.
Most chromatographic methods for detection of influenza virus which are currently commercially available are based on methods for assaying the presence or absence of influenza virus in a sample by detection of nucleoprotein (NP). However, these methods cannot necessarily be said to have sufficient detection sensitivity, and detection of influenza virus by these methods is difficult in cases where the sample is derived from a patient within 6 hours after occurrence of fever. Therefore, further improvement of the detection sensitivity has been demanded.
Well-known examples of proteins constituting influenza virus include HA protein, NA protein, nucleoprotein (NP), and matrix proteins 1 and 2 (M1 and M2). The protein present in the largest number in each influenza virus particle is M1 protein. The amount of M1 protein is reported to be about 3 times larger than that of NP protein (Non-patent Document 1).
Surfactant treatment of samples to be subjected to immunoassays is known as described in Patent Document 1 and Patent Document 2.